We are investigating in Dictoyostelium the mechanisms which control the expression of enzymes whose synthesis increases during development. Although the enzyme UDP glucose prrophosphorylase (UDPGP) plays a major role in completion of normal development it is only a minor fraction of the cellular proteins. This makes it difficult to characterize the enzyme at different developmental stages and to develop assays for its mRNA. To overcome these problems we have developed a novel procedure for identifying proteins in high resolution denaturing gels. It has allowed us to identify UDPGP from vegative cells as a single discrete species in crude extracts and to show that a new form accumulates which accounts for the increase in enzyme activity during differentiation. We are using these procedures in developing assays of the mRNA of UDPGP. The assays are being used to determine the origin of the observed heterogeneity and the mechanism of increase in synthesis of the enzyme. Finally the assays are being used to clone the gene to identify bacterial colonies which contain Dictyostelium DNA complementary to the UDPGP mRNA.